Introduction to version control with Git

Day 2: Branching, Merging and collaboration workflows

Selina Baldauf

September 19, 2023

Before we start

Did everyone accept a collaboration invitation?

Recap

Basic Git workflow:

  1. Initialize a Git repository
  2. Work on the project
  3. Stage and commit changes to the local repository
  4. Push to the remote repository

Recap

Basic Git workflow:

  1. Initialize a Git repository
  2. Work on the project
  3. Stage and commit changes to the local repository
  4. Push to the remote repository

Recap

Git is a distributed version control system

  • Idea: many local repositories synced via one remote repo
  • Collaborate with
    • yourself on different machines
    • your colleagues and friends
    • strangers on open source projects

Get a repo from a remote

  • In Git language, this is called cloning
    • Get a full copy of the remote repo

Get a repo from a remote

  • To clone a repo, you need to know the repo’s URL

  • You can clone all public repositories
    • You can only push if you are authorized
  • You can clone private repositories if you are a collaborator

Now you

Clone your team mate’s cook Book repo (File -> Clone repository)
It should be in the list of your repositories if you accepted the invitation.

Get changes from the remote

  • Local changes, publish to remote: git push
  • Remote changes, pull to local: git pull

A simple collaboration workflow


  • One remote repo on Github, multiple local repos
  • Idea: Everyone works on the same branch
    • Pull before you start working
    • Push after you finished working

A simple collaboration workflow


This works well if

  • Repo is not updated often
  • You don’t work on the same files simultaneously
  • No need to discuss changes before they are integrated
  • You collaborate with yourself

A simple collaboration workflow


This workflow starts to be problematic when

  • People push often/forget to pull regularly
    • Potential conflicts on main
  • You just want to experiment
    • Everything goes directly to main

Let’s give it a try

  • Make sure you are in the repository of your team mate
  • Open a recipe in the cook book of your team mate
    • Repository -> Show in Explorer
  • Change something in there
  • Commit the change and push it

Get the changes of your team mate from the remote.

  • Switch to your own cook book repository
  • Pull the changes (Same button as the push button)
  • Have a look at the commit history to see what changed

A branching-merging workflow


  • One remote repo on Github, multiple local repos
  • Idea: Everyone works on the their separate branch
    • Merge branch with the main when work is done

A branching-merging workflow


Advantages of this approach

  • Guarantee that main always works
  • Potential conflicts don’t have to be solved on main
  • You can experiment without messing up the main

Working on a separate branch

The steps to create and work on a separate branch are easy:

  • Create a local branch and switch to it
  • Work on the branch like you are used to
    • Make changes, stage and commit

Merging changes from a branch

To bring changes to the main branch you need to merge them.

Normally: Git merge brings the commits from the branch to main

Merging changes from a branch

To bring changes to the main branch you need to merge them.

If there was a commit on a common file in main, a merge commit is introduced.

Merging changes from a branch

To bring changes to the main branch you need to merge them.

  • Mostly merging happens without problems, but…
  • … if the same line was edited on separate branches…
  • … there will be a merge conflict 😱

Merge conflicts need to be solved manually. You need to chose which of the conflicting versions you want to keep.

Now you

Create a branch and merge it in your team mate’s cook book
Complete task 2 “Branch and merge” (10 min)

A branching-merging workflow with Github

  • One remote repo on Github, multiple local repos
  • Idea: Everyone works on the their separate branch
    • Merge branch with the main when work is done

A branching-merging workflow with Github

  • One remote repo on Github, multiple local repos
  • Idea: Everyone works on the their separate branch
    • Merge your branch with the main when you are finished
    • Create a pull request on Github to ask for a merge

A branching-merging workflow with Github

A pull request is basically asking your collaborators:

What do you think of my changes? Can we integrate them in main or do we still need to change something?

Github has nice features for pull requests:

  • Describe your changes in detail
  • Collaborators can easily compare versions
  • Collaborators can discuss and comment on your changes
  • …

A pull request is merged on Github when everyone agreed on the code.

Now you

Create a pull request on your partners repo
Complete task 3 “Pull requests” (10 min)

Thanks for your attention

Questions?

Next week

  • Monday 2.30 - 3.30 on Webex (link via email)

  • Until then: work with Git on your own (~ 1 - 2 h)

    • Pick something you find most interesting/useful to you

  • Collect questions/problems/discoveries

  • More Git topics

Some ideas

  • Start working with Git on one of your research projects
  • Publish one of your projects on Github including a nice README
  • Practice collaboration by contributing to my cook book project
    • Accept the invitation I’ll send you later and work with branches and pull requests
    • I will answer your pull requests and request some changes :)
  • Check out the How-To guides if you want to
  • If you find a mistake on my websites
    • Edit the page on Github or report an issue
  • …

Branching, Merging and Collaboration with Git